Help End Marijuana Prohibition (HEMP) launches its campaign for the Western Australia Senate in Perth with a giant inflatable cannabis joint on Tuesday.

HEMP, a micro party with 6,000 members, is expected to have the lead on voting preferences according to political experts. With this, the legalisation of marijuana became the main issue surrounding the upcoming re-election.

The party claimed that WA Greens Senator Scott Ludlam is being socially conservative on the issue of marijuana and other drugs.

''The Australian Greens do not support the legalisation of currently illegal drugs," as stated on Section 8 of the Green's federal policy document on "drugs, substance abuse and addiction."

Hence, HEMP abandoned the Greens and preferred Labor for the upcoming re-election.

''The Greens take votes away from us because people just assume they are for cannabis law reform,'' HEMP's lead WA candidate Jim Moylan said, adding that the Greens were "a joke on cannabis law reform."

Mr Ludlam said that being tagged a social conservative was acceptable so long as he is doing the right thing.

Mr Ludlam rejected the social conservative tag. ''If supporting a harm-minimisation approach to illegal drug use and advocating the legalisation of medical cannabis is conservative then so be it. In an environment where the old parties refuse to engage with the issue and continue to ignore the advice of health and law enforcement professionals, the Greens have consistently spoken out when the opportunity presents itself. My colleague Senator Richard Di Natale has reconstituted the Parliamentary Group for Drug Law Reform and the Greens will continue to work with the community for law reform," Mr Ludlam said.

On Saturday, the Greens launched its campaign through a flash mob in a city mall in Perth.

Mr Ludlam called for people's vote to be able to return to the parliament.

"What we know is that the margin can be down to 14 votes at one stage, that was how it hung on the balance. What it tells me is people's vote is very powerful, that you can't take it for granted, and we'll be working hard for every single vote. I'm very confident in the strength of our team and the effort we're putting in."